Method and system for measuring water hardness

ABSTRACT

Prior to adding detergent or chelant, the conductivity of water in a washing chamber is measured. The maximum concentration of hard water ions that could correspond to the measured conductivity is determined, i.e., it is assumed that all of the conductivity is from calcium and/or magnesium ions in the water even though other ions may in fact be contributing to the measured conductivity. Enough chelating agent is added to the chamber to sequester this maximum concentration of hard water ions and the conductivity is measured again. Using the two conductivity measurements, the actual concentration of hard water ions is determined. A chelant factor based on the actual concentration of hard water ions is then used to determine the amount of chelant to be added for subsequent wash cycles to sequester all of the hard water ions.

TECHNICAL FIELD

The present invention relates generally to measuring water hardness, andin particular to measuring, and compensating for, water hardness in awashing machine.

BACKGROUND

Machine washing systems typically employ cleaning agents that form acleaning solution when mixed with water. Cleaning agents, such asdetergents, breakdown and remove food or other soils and operate mosteffectively in alkaline environments. However, hard water ions (e.g.,calcium and magnesium ions) present in the water supply of the washerwill reduce the effectiveness of the detergent. Thus, chelating agentsare added to the wash water to sequester the hard water ions. Typicalchelants include, without limitation, nitrilotriacetic acid (NTA),ethylene diamene tetraacetic acid (EDTA) and tripolyphosphate (TPP).

The water hardness (i.e., the concentration of hard water ions) istypically not known prior to beginning a wash operation, so the amountof chelant that needs to be added to the wash water to sequester thehard water ions is also not known.

One approach to account for unknown water hardness is to add an excessamount of chelating agent to the detergent to sequester all possiblehard water ions. However, this approach typically wastes a large amountof chelant. In addition, this approach is costly because chelatingagents are expensive.

Two approaches to determining when enough chelant has been added tocompletely sequester the hard water ions are described in U.S. Pat. No.4,334,881, entitled “Method and Apparatus for Automatic End-PointDetection in Tripolyphosphate Sequestration of Hardness.” In oneapproach, TPP is slowly added to the wash water while the electricalconductivity of the wash water is monitored. Complete sequestration isdetermined by detecting when the maximum rate of change of conductivitywith chelant addition occurs. In the second approach, if the pH of thewashing solution is above 11 (to precipitate the magnesium ions), whenthe conductivity first increases substantially with TPP addition, 1.5times more TPP is added to sequester all of the remaining calcium ions.Both of these approaches, however, tend to be quite slow and inaccurate.

Thus, there is a need for improved methods and systems to measure waterhardness and to determine the amount of chelating agent needed tosequester hard water ions.

SUMMARY

The present invention overcomes the limitations and disadvantagesdescribed above by providing methods and systems to measure waterhardness and to determine and dispense the amount of chelating agentneeded to sequester the hard water ions.

In one embodiment, a method for dispensing a chelant and a cleaningagent includes obtaining a first conductivity measurement anddetermining a first chelant amount based on the first conductivitymeasurement. The first chelant amount is added to a chamber from achelant source and a second conductivity measurement is obtained. Basedon the second conductivity measurement, a chelant factor is determinedand stored. An amount of detergent is added to the chamber from adetergent source.

In another embodiment, a method for detecting a change in water hardnessincludes obtaining a first conductivity measurement and determining afirst chelant amount based on the first conductivity measurement. Thefirst chelant amount is added to a chamber from a chelant source and asecond conductivity measurement is obtained. Based on the secondconductivity measurement, a current chelant factor is determined. Achange in the water hardness is based on comparing the current chelantfactor and a previous chelant factor.

In still another embodiment, a method for detecting a change in waterhardness includes adding chelant during each of a plurality ofprocessing cycles to a chamber to sequester water hardness ions. Arespective chelant factor is determined, where the chelant factor isrelated to water hardness for the respective processing cycle. Therespective chelant factor for a current processing cycle is comparedwith at least one earlier determined chelant factor. When the comparingindicates a change in water hardness satisfying predefined criteria, asignal is generated.

In still another embodiment, a method for identifying a decrease inwater softening effectiveness includes obtaining a first conductivitymeasurement and determining a first chelant amount based on the firstconductivity measurement. A first portion of the first chelant amount isadded to a chamber from a chelant source and a second conductivitymeasurement is obtained. An effectiveness of water softening isdetermined and a second portion of the first chelant amount is added tothe chamber from the chelant source based on the effectiveness. A thirdconductivity measurement is obtained and a chelant factor based on thethird conductivity measurement is determined and stored.

The value in knowing the water hardness is related to the potential toeliminate problems caused by uncontrolled water hardness and to reduceoveruse of chelants. Water hardness can change for a variety of reasons,including changes in water supply sources, seasonal changes in aquifers,and water softener failures. This invention makes it is possible toeasily detect these changes and to adjust the chelant accordingly,thereby saving chemical costs and improving wash results.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned embodiments of the invention, as well as additionalaspects and embodiments thereof will be more clearly understoodhereinafter as a result of a detailed description of embodiments of theinvention when taken in conjunction with the drawings. Like referencenumerals refer to corresponding parts throughout the several views ofthe drawings.

FIG. 1 is a schematic diagram illustrating an exemplary washing systemaccording to an embodiment of the invention.

FIG. 2 is a block diagram illustrating a control system according to anembodiment of the invention.

FIG. 3 is a flow chart of an exemplary process for measuring waterhardness and dispensing a chelant and a cleaning agent according to anembodiment of the invention.

FIGS. 4A and 4B are schematic graphs of electrical conductivity versushard water ion concentration and electrical conductivity versus amountor concentration of chelating agent, respectively.

FIG. 5 is a flow chart of an exemplary process for measuring waterhardness, dispensing a chelant and a cleaning agent, and identifying adecrease in water softening effectiveness according to an embodiment ofthe invention.

DESCRIPTION OF EMBODIMENTS

Water hardness is measured in a novel manner using an electricalconductivity sensor, one or more chelating agents, and acomputer-controlled chemical dispensing system.

In some embodiments, an initial conductivity measurement of water in awashing chamber is made when a new fill cycle is detected. The maximumconcentration of hard water ions that could correspond to the measuredconductivity is determined, i.e., it is assumed that all of theconductivity is due to calcium and/or magnesium ions in the water eventhough other ions may in fact be contributing to the measuredconductivity. Enough chelating agent is then added to the chamber tosequester this maximum concentration of hard water ions and theconductivity is measured again. Using the two conductivity measurements,the actual concentration of hard water ions is determined. A chelantfactor based on the actual concentration of hard water ions is then usedto determine the amount of chelant to be added for each subsequent washcycle to sequester all of the hard water ions.

Methods, systems, and computer programs are described that measure waterhardness and that determine and dispense the amount of chelating agentneeded to sequester hard water ions. Reference will be made to certainembodiments of the invention, examples of which are illustrated in theaccompanying drawings. While the invention will be described inconjunction with the embodiments, it will be understood that it is notintended to limit the invention to these particular embodiments alone.On the contrary, the invention is intended to cover alternatives,modifications and equivalents that are within the spirit and scope ofthe invention as defined by the appended claims.

Moreover, in the following description, numerous specific details areset forth to provide a thorough understanding of the present invention.However, it will be apparent to one of ordinary skill in the art thatthe invention may be practiced without these particular details. Inother instances, methods, procedures, and components that are well knownto those of ordinary skill in the art are not described in detail toavoid obscuring aspects of the present invention.

FIG. 1 is a schematic diagram illustrating an exemplary washing systemaccording to an embodiment of the invention. Washing system 100 includesa washing chamber 102, a control system 104, a cleaning agent dispenser106, a chelant dispenser 108, and a water supply 110. In someembodiments, washing system 100 is a commercial dishwasher. In otherembodiments, washing system 100 is a consumer dishwasher, a commercialclothes washer, or a consumer clothes washer.

Washing chamber 102 is a connected to a drain 112.

Control system 104 is connected to meter 114, conductivity sensor 118,cleaning agent dispenser 106 and chelant dispenser 108. Meter 114monitors the flow of water from water supply 110 into washing chamber102.

Conductivity sensor 118 can be a typical sensor that is normally used tomeasure the detergent concentration in a commercial dishwasher. Detailson this type of sensor and the electronics and control associated withit are described in U.S. Pat. Nos. 6,223,129 and 6,529,841, the contentsof which are hereby incorporated by reference. Other types ofconductivity measurement systems will also work. Conductivity sensor 118may also include a temperature sensor so that raw conductivitymeasurements can be compensated back to 20° C. using the standard 1.8%/°C. compensation factor.

Dispensers 106 and 108 are similar to those used to dispense chemicalsinto a commercial dishwasher. Exemplary dispensers are described in U.S.Pat. No. 5,647,391, the contents of which are hereby incorporated byreference. The chemical forms of the cleaning agent and the chelant maybe either liquid or solid (powder). Control system 104 should be capableof controlling the addition of the chemicals in accurate dose amounts.Typical dose amounts are between 5 cc's (or 5 grams) and 250 cc's (or250 grams). Typical accuracy should be +/−5% of the target dose amount,or +/−1 cc, or +/−1 gram). These numbers and accuracies are for typicalcommercial dishwashers and should not be considered as limits on thescope of the invention.

The chemicals serve two purposes. Their primary role is to support thecleaning process of the dishwasher. Their secondary role is as reagentsfor water hardness measurements. In some embodiments, the detergent issplit into two separate chemicals; one contains the primary cleaningingredients and the other contains the chelant. The chelant is used tocontrol (sequester) the hard water ions. To create a complete detergent,the cleaning chemical, often called the “chemical energy” or “CE”component, is added to the wash tank to a concentration level determinedby the soil levels that will be present (less if light soil is mostprobable and more if heavy soil is more likely). The chelant, oftencalled the “chelation value” or “CV” component, is added to aconcentration level that will sequester all of the hardness ions. Sincethe CV component is quite costly, it is most cost effective to not dosemore chelant than is required.

FIG. 2 is a block diagram illustrating a control system according to anembodiment of the invention. Control system 104 typically includesprocessing unit (CPU) 222, one or more network or other communicationsinterfaces 232, memory 202, and one or more communication buses 224 forinterconnecting these components. Control system 104 optionally mayinclude a user interface 116 comprising a display device 228 and akeyboard 230. Memory 202 may include high speed random access memory andmay also include non-volatile memory, such as one or more magnetic diskstorage devices. Memory 202 may optionally include one or more storagedevices remotely located from the CPU 222. In some embodiments, thememory 202 stores the following programs, modules and data structures,or a subset thereof:

-   -   an operating system 204 that includes procedures for handling        various basic system services and for performing hardware        dependent tasks;    -   a communication module 206 that is used for connecting control        system 104 to other computers (e.g., for remote monitoring of        washing system 100) or devices via one or more communication        interfaces 232 (wired or wireless); the communication interfaces        may include a network interface (for connecting to the Internet,        a local area network, or the like), an RS232 interface, or any        other suitable interface;    -   water control module 208 that regulates the amount of water in        chamber 102;    -   a chelant control module 210 that regulates the amount of        chelant added to chamber 102 by dispenser 108;    -   a detergent control module 212 that regulates the amount of        cleaning agent added to chamber 102 by dispenser 106;    -   a conductivity sensor module 214 that controls or monitors the        operation of sensor 118;    -   a hardness calculation module 216 that determines hard water ion        concentrations and chelant dose amounts based at least in part        on conductivity measurements and water volume;    -   a comparison module 218 that compares current hard water ion        concentrations and/or chelant factors with previous values to        identify changes in water hardness and/or water softener        effectiveness; and    -   a wash module 220 that controls the washing process in chamber        102.

Each of the above identified modules corresponds to a set ofinstructions for performing a function described above. These modules(i.e., sets of instructions) need not be implemented as separatesoftware programs, procedures or modules, and thus various subsets ofthese modules may be combined or otherwise re-arranged in variousembodiments. In some embodiments, memory 202 may store a subset of themodules and data structures identified above. Furthermore, memory 202may store additional modules and data structures not described above.

FIG. 3 is a flow chart of an exemplary process for measuring waterhardness and dispensing a chelant and a cleaning agent according to anembodiment of the invention.

Control system 104 determines if a new fill cycle for washing system 100has occurred (302). In a new fill cycle, chamber 102 is filled withclean water from supply 110 prior to the start of washing. Variousmethods can be used to sense when chamber 110 has been drained andrefilled with clean water. U.S. Pat. No. 4,509,543 describes a methodthat uses a conductivity sensor, such as sensor 118. Alternatively, afloat switch could be used to sense a tank drain and refill. If a newfill cycle has occurred, a first conductivity measurement of the (clean)water is obtained (304), for example by conductivity sensor module 214using sensor 118.

The first conductivity measurement is converted to a maximum hard waterion concentration (306). In some embodiments, hardness calculationmodule 216 uses an equation or lookup table relating conductivity tohard water ion concentration to make the conversion. FIG. 4A is aschematic graph of electrical conductivity versus hard water ionconcentration at a particular temperature. The data for such a graph(and the corresponding equations or lookup table) can be obtained bymeasuring the conductivity of initially pure water samples as knownamounts of hard water ions are added. These measurements can also bedone at a series of temperatures so that the temperature dependence ofthe conductivity can be accounted for. Thus, a first conductivitymeasurement (e.g., A in FIG. 4A) can be converted to a maximum possiblehard water ion concentration (e.g., B in FIG. 4A). Hard water ionconcentrations are typically expressed in ppm (parts per million) ofcalcium ions.

Based on the first conductivity measurement, an amount of chelant to beadded to the water in chamber 102 is determined (308). In someembodiments, the chelant amount is an amount that is projected to besufficient to fully sequester water hardness ions in the chamber. Forexample, if a 1:1 molar ratio of chelant to hard water ions is needed tofully sequester the hard water ions, then the amount of chelant neededis given byChelant volume=(maximum possible hard water ion concentration)·(volumeof water in chamber)

The amount of chelant needed can also be expressed as a mass bymultiplying the preceding equation by the appropriate density.

In some embodiments, hardness calculation module 216 calculates thechelant amount required based on the maximum possible hard water ionconcentration (derived from the first conductivity measurement) and theamount of water that meter 114 determines has gone into chamber 102during the new fill cycle.

The calculated chelant amount is added to chamber 102 from chelantsource 108 (310). The chelant can be added with a peristaltic meteringpump (or any other suitable liquid pump) if the chelant is a liquid orwith a powder measuring device (also called a powder metering device) ifthe chelant is a powder. After the chelant is thoroughly mixed with thewater in chamber 102, a second conductivity measurement is obtained(312). Complete mixing can be sensed by monitoring for stability in theconductivity measurement. Alternately, the system can wait a predefinedamount of time after the dispensing operation to perform the secondconductivity measurement.

Based on the second conductivity measurement, the actual hard water ionconcentration is determined (314). This determination can be explainedwith the aid of FIG. 4B, which is a schematic graph of electricalconductivity versus the amount of chelating agent added for threedifferent water samples with the same initial conductivity (A in FIG.4B), but different actual hard water ion concentrations.

As shown in U.S. Pat. No. 4,334,881, the conductivity increases slowlywith added chelant until the hard water ions are fully sequestered. Fullsequestration typically occurs at a 1:1 molar ratio of hard water ionsto chelant elements. Once the hard water ions are fully sequestered, theconductivity rises more rapidly with additional chelant, at about thesame rate as would occur in water containing no hard water ions. Thisbehavior explains the change in slope in lines 402 and 404. The slopeafter complete sequestration may depend on which chelant is being added.This slope may be determined by adding chelant to pure water samples andmeasuring the change in conductivity.

Line 404 shows schematically the conductivity behavior for a watersample where the actual hard water ion concentration is theconcentration derived from the first conductivity measurement (i.e., Bderived from A in FIG. 4A). In other words, for this sample, theassumption that essentially all of the conductivity is due to hard waterions is correct. Consequently, for this sample, the amount of chelatingagent added (C in FIG. 4B) is just enough to fully sequester the hardwater ions; the second conductivity measured is D in FIG. 4B; and noexcess chelant is wasted.

Line 400 shows schematically the conductivity behavior expected for awater sample where the hard water ion concentration is negligible. Inother words, for this sample, all of the conductivity is due to ionsother than hard water ions. For this sample, no chelating agent isneeded because there are no hard water ions to sequester. Consequently,there is no slow increase in conductivity for this sample. Instead, theconductivity rises rapidly as soon as chelant is added to the water,ending up at F in FIG. 4B when the amount of chelant added is C.

Line 402 shows schematically the conductivity behavior expected for awater sample where the hard water ion concentration is not negligible,but is less than the concentration derived from the first conductivitymeasurement. In other words, for this sample, only part of theconductivity is due to hard water ions. For this sample, the amount ofchelating agent needed to sequester the hard water ions is G in FIG. 4B.When the amount of chelant added to this sample is C, then somechelating agent (i.e., C-G in FIG. 4B) is wasted and the second measuredconductivity is E in FIG. 4B.

The second conductivity measured for samples with only a portion of theconductivity due to hard water ions varies in an approximately linearmanner between F (no conductivity due to hard water ions) and D (allconductivity due to hard water ions) in FIG. 4B. Thus, if the slopesbefore and after complete sequestration are known for a given chelatingagent (e.g., from prior conductivity measurements on water samples withcontrolled chelant concentrations) and the conductivities before andafter addition of the chelating agent are measured, the secondconductivity measurement can be converted to the actual hard water ionconcentration. In some embodiments, the conductivity versus amount ofchelant slopes before and after complete sequestration are stored forone, or two or more chelants in memory 202 and used by hardnesscalculation module 216 to convert the second measured conductivity to anactual hard water ion concentration.

In one embodiment, conductivity measurements were made at 20° C.,resulting in the determination of the following first-orderrelationships:

In FIG. 4A:B=1.14×A

where

-   -   A=clean water conductivity, in uS/cm, and    -   B=maximum possible hard water ion concentration, ppm calcium        ions.

In FIG. 4B:D=1.25×AandF=(1.65×A)+304 uS/cm

where

-   -   A=the clean water conductivity, in uS/cm,    -   D=the conductivity measured after an amount of chelant C is        added and mixed when all of the initial conductivity was due to        hard water ions, and    -   F=the conductivity measured after an amount of chelant C is        added and mixed when none of the initial conductivity was due to        hard water ions.

These equations, in conjunction with the two conductivity measurements(i.e., the clean water conductivity and the conductivity measured afterthe chelant is added and mixed) can also be used to calculate the actualhard water ion concentration.

In some embodiments, tables are used, rather than equations, tocalculate the actual hard water ion concentration. In the tables, foreach starting conductivity (interpolation can be used to keep the tablesize reasonable), there is an array of possible ending conductivitiesthat relate to the percentage of the maximum possible hard water ionconcentration. The range would extend from 100% to 0%. In other words,while the maximum possible hard water ion concentration may have been700 ppm, the second conductivity measurement may indicate that only 30%of the ions were hard water ions and that the actual hard water ionconcentration is only 210 ppm. Table 1 is an exemplary table.

TABLE 1 Table for converting conductivity after chelant addition to hardwater ion concentration for a starting conductivity of 600 uS/cm, at 20°C. Ending Conductivity, Percent of maximum possible Actual hard waterion uS/cm hard water ion concentration concentration, ppm 760 100 700898 75 525 1036 50 350 1173 25 175 1310 0 0

In some embodiments, the actual hard water ion concentration can becompared to previous measurements to detect a significant change in thehard water ion concentration (316), for example by using comparisonmodule 218. More specifically, the actual hard water ion concentrationdetermined at each refilling of the water tank may be compared with oneor more previously hard water ion concentrations determined at priorrefillings of the water tank. Alternately, the current hard water ionconcentration determination may be compared with an average of two ormore previously hard water ion concentrations. A significant change inthe hard water ion concentration determination (e.g., an increase of Npercent, such as 20 percent, or an increase of a predefined amount, suchas 150 ppm) may indicate a failure of a water softener device, or mayindicate another condition or problem requiring the attention of arepair person. When the comparison at 316 indicates that the currenthard water ion concentration is significantly higher than prior hardwater ion concentration determinations, a remedial action maybeinitiated. The remedial action may include turning on a warning light,sending a message to another device or to a particular email address orthe like, or other appropriate action. In one embodiment, the remedialaction is undertaken only when the new, higher hard water ionconcentration determination is confirmed during a subsequent refillingof the water tank.

In some embodiments, the change in water hardness at 316 is detected bycomparing a chelant factor computed (318) for a current water fill cyclewith the chelant factor computed for one or more prior water fillcycles, and determining whether the difference (if any) exceeds apredefined threshold. In these embodiments, and in some otherembodiments as well, detection operation 316 occurs after thecalculation of the chelant factor at 318.

An amount of chelant needed to sequester the actual hard water ionconcentration is calculated (318). In some embodiments, this calculationuses a chelant factor. As used herein, a chelant factor is a multiplierused in the calculation of the amount of chelant needed forsequestration that compensates for the fact that only a portion of themeasured conductivity may be due to hard water ions. The chelant factorincorporates or corresponds to the fraction of the water conductivitythat is actually due to hard water ions. If a 1:1 molar ratio of chelantto hard water ions is needed to fully sequester the hard water ions,then the amount of chelant needed when additional water is added tochamber 102 is given by:Chelant volume=(chelant factor)(maximum possible hard water ionconcentration)(incremental volume of water added to chamber)

If a molar ratio other than 1:1 is needed for a particular chelant tofully sequester the hard water ions, this ratio can be incorporated intothe chelant factor. More generally, the chelant factor is a multiplierfor determining the amount of chelant (by volume or weight) needed tofully sequester the hard water ions based on a conductivity measurementand the incremental amount of water. Thus, in some embodiments, thechelant factor may also incorporate a conversion factor that relates ameasured conductivity to a maximum possible hard water ionconcentration.

For line 402 in FIG. 4B, the chelant factor is G/C or, equivalently,(F-E)/(F-D). The chelant factor, which is based on the secondconductivity measurement, the first conductivity measurement, and theconductivity slopes before and after complete sequestration, isdetermined and stored in memory 202 (e.g., by hardness calculationmodule 216).

An amount of detergent is added (320) to chamber 102 from a detergentsource, such as cleaning agent dispenser 106, and washing (322) isperformed by washing system 100.

In some embodiments, such as commercial washing machines, chamber 102 isnot completely drained and refilled with water between each wash cycle.Instead, an incremental amount of water is added to chamber 102 that, inturn, needs an incremental amount of chelating agent and detergent addedas well. In such cases, control system 104 determines that there is nota new fill cycle (302).

The incremental amount of water added from water supply 110 to chamber102 is determined, for example using meter 114. A second chelant amountin accordance with the amount of added water and the chelant factor isdetermined using the equation given above. The second chelant amount isadded to chamber 102 from chelant source 108 (324).

In addition, an incremental amount of detergent is added (320) tochamber 102 from a detergent source, such as cleaning agent dispenser106, and additional washing (322) is performed by washing system 100.

In some embodiments, with each new fill cycle, a current chelant factoris determined based on a second conductivity measurement, a firstconductivity measurement, and the conductivity slopes before and aftercomplete sequestration, using the process described above. A change inwater hardness is determined based on the current chelant factor and aprevious chelant factor. An increase in water hardness is identifiedwhen the current chelant factor is greater than the previous chelantfactor.

In some embodiments, during each of a plurality of processing cycles,chelant is added to a chamber to sequester water hardness ions and achelant factor is determined for each processing cycle using the processdescribed above. As explained above, each chelant factor relates to thewater hardness for the respective processing cycle. The chelant factorfor a current processing cycle is compared with at least one earlierdetermined chelant factor. When the comparison indicates a change inwater hardness satisfying some predefined criteria, a signal such as avisual and/or auditory alarm, or an electronic message transmitted toanother device, is generated. In some embodiments, the predefinedcriteria include the change in chelant factor being greater than apredefined amount.

The water hardness measurement processes described above are based onadding an amount of chelant equal to the maximum that could possibly berequired (308 and 310). In most cases, this will not cause a large wasteof chelant because it is only done once for each tank drain and fillcycle and because the ions in the clean water will typically be mostlyhard water ions. However, an exception to the typical case occurs whenan ion exchange water softener is used. When the water softener isworking properly, most of the ions will be sodium and not requiresequestering. As described below with respect to FIG. 5, control system104 and the hardness measurement process can be made to detect that asoftener is employed. If softener use is detected, then control system104 adds only a fraction of the calculated maximum chelant dose(308/508). If the conductivity rises at a rate that indicates thesoftener is working, then no more chelant is added. If the conductivityrises slowly with chelant, indicating at least moderate hardness, thenthe rest of the chelant dose is added and the normal hardnessmeasurement is performed. In some embodiments, control system 104detects that a softener is in use if the percentage of actual hardnesscalculated in the normal measurement is less than 25% of the potentialmaximum hard water ion concentration. This embodiment could also beuseful in cases where there is a natural occurrence of non-hard waterions with few hard water ions present.

FIG. 5 is a flow chart of an exemplary process for measuring waterhardness, dispensing a chelant and a cleaning agent, and identifying adecrease in water softening effectiveness according to an embodiment ofthe invention. This process builds on the exemplary process shown inFIG. 3 and discussed above, so analogous steps or operations that arealready explained in detail above will only be briefly discussed here.

Control system 104 determines if a new fill cycle for washing system 100has occurred (502). If so, a first conductivity measurement of the washwater is obtained (504). The first conductivity measurement is convertedto a maximum hard water ion concentration (506). Based on the firstconductivity measurement, an amount of chelant to be added to the waterin chamber 102 is determined (508). In some embodiments, the chelantamount is an amount that is projected to be sufficient to fullysequester water hardness ions in the chamber.

Control system 104 determines if a softener is present (526). In someembodiments, this determination can be made based on a previousmeasurement of water hardness finding less than a predetermined amountof the conductivity due to hard water ions (e.g., less than 25%). Insome embodiments, this determination can be made based on user input(e.g., a flag or other value may be stored in the control system 104based on a user input to the control system).

If softener is known or believed to be present, just a portion of thecalculated maximum chelant dose is added to chamber 102 (528) fromchelant dispenser 108. After thoroughly mixing the added chelant, asecond conductivity measurement is obtained (530). In some embodiments,the amount of chelant added at 528 is sufficient to distinguish betweenwater having a low, expected concentration of hard water ions (e.g., aconcentration similar to what was determined during one or more previouswater cycles, or a predetermined concentration consistent with the useof a water softener) and water having an unexpectedly high concentrationof hard water ions. This amount of chelant will typically be much less(e.g., at least 50 percent less) than the amount of chelant that wouldbe required if all the ions contributing to the measured conductivitywere attributable to hard water ions.

In some embodiments, the effectiveness of the water softening isdetermined as follows. If the added chelant creates a rapid rise inconductivity, the softener is working properly (532) and no more chelantneeds to be added. The detergent is added (520) and washing begins(522).

Conversely, if the added chelant creates a slow rise in conductivity,the softening is not effective (532) and a second portion of the maximumchelant dose is added to chamber 102 (534). In some embodiments, thesecond portion equals the maximum chelant dose less the first chelantportion (i.e., the second portion is the remaining amount of the maximumchelant dose). After thoroughly mixing the added chelant, a thirdconductivity measurement is made (512) and the actual hard water ionconcentration is determined (514). In some embodiments, control system104 detects that a softener is in use if the percentage of actualhardness calculated in the normal measurement is less than apredetermined amount (e.g., less than 25%) of the maximum possible hardwater ion concentration (516). An amount of chelant needed to sequesterthe actual hard water ion concentration is calculated (518). Asexplained above, this calculation uses a chelant factor in someembodiments. The chelant factor based on the third conductivitymeasurement is determined (e.g., by hardness calculation module 216) andstored (e.g., in memory 202). The detergent is added (520) and washingbegins (522).

If softener is not known or believed to be present (526), the calculatedmaximum chelant dose is added to chamber 102 (510). After thoroughlymixing the added chelant, a conductivity measurement is made (512) andthe actual hard water ion concentration is determined (514). In someembodiments, control system 104 detects that a softener is in use if thepercentage of actual hardness calculated in the normal measurement isless than a predetermined amount (e.g., less than 25%) of the maximumpossible hard water ion concentration (516). An amount of chelant neededto sequester the actual hard water ion concentration is calculated(518). As explained above, this calculation uses a chelant factor insome embodiments. The detergent is added (520) and washing begins (522).

If this is not a new fill cycle (502), an incremental amount of water isadded to chamber 102 that, in turn, needs an incremental amount ofchelating agent and detergent added as well. The incremental amount ofwater added from water supply 110 to chamber 102 is determined, forexample using meter 114. A second chelant amount in accordance with theamount of added water and the chelant factor is determined using theequation given above. The second chelant amount is added to chamber 102from chelant source 108 (524). An amount of detergent is added (520) tochamber 102 from a detergent source and washing (522) is performed bywashing system 100.

In addition to detecting and compensating for a failed water softener,control system 104 can also warn the user that it is time to rechargethe water softener. Control system 104 can automatically increase thechelant feed from dispenser 108 while the softener is “leaking hardwater” and then decrease it when the softener system or device has beenserviced and restored to normal operation.

In some embodiments, the determinations at 526 and 516 may also be usedto detect the presence of soft water, with low hard water ionconcentrations, even when a softener system is not in use. By detectingthat the washing system is receiving soft water, the amount of chelantused at the beginning of each fill cycle may be significantly reduced(e.g., by 50 percent or more).

In some embodiments, to reduce the amount of chelant wasted by repeateddeterminations of the chelant factor, a new chelant factor determinationis performed only once every N fill cycles, where N is equal to 2, 3, 4or other larger number. In some other embodiments, when the chelantfactor is below a threshold value (e.g., below a value corresponding to50% of the ions comprising hard water ions), the chelant factor isassumed to be correct from one fill cycle to the next, but is tested atthe beginning of each new fill cycle, or each Nth new fill cycle. Thechelant factor is tested or checked by adding an amount of chelant thatfalls between a low value corresponding to the previously determinedchelant factor and a high value corresponding to the amount of chelantthat would be needed if all the ions associated with the currentconductivity measurement were hard water ions, and then taking a newconductivity measurement, computing a new chelant factor and comparingthe new chelant factor with the previously computed chelant factor. Byusing less chelant than the aforementioned high value, the total amountof chelant used is reduced. In all of these embodiments, a singlechelant dispensing event or operation is used for each wash cycle,except in the rare situations in which a water softener system hasfailed or a significant change in water hardness is detected.

Although some of various drawings illustrate a number of logical stagesin a particular order, stages which are not order dependent may bereordered and other stages may be combined or broken out. While somereordering or other groupings are specifically mentioned, others will beobvious to those of ordinary skill in the art and so do not present anexhaustive list of alternatives. Moreover, it should be recognized thatthe control system could be implemented in hardware, firmware, softwareor any combination thereof.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A method for dispensing a chelant and a cleaning agent, comprising:obtaining a first conductivity measurement; determining a first chelantamount based on the first conductivity measurement; adding the firstchelant amount to a chamber from a chelant source; obtaining a secondconductivity measurement; determining a chelant factor based on aplurality of values, including the first conductivity measurement, thesecond conductivity measurement, and the first chelant amount, whereinthe chelant factor corresponds to a fraction of water conductivity dueto hard water ions; storing the chelant factor; adding an amount ofdetergent to the chamber from a detergent source; and after storing thechelant factor: determining an additional amount of water added to thechamber; determining a second chelant amount in accordance with theadditional amount of added water and the chelant factor; and adding thesecond chelant amount to the chamber.
 2. The method of claim 1,including determining as the first chelant amount an amount of chelantthat is projected to be sufficient to fully sequester hard water ions inthe chamber.
 3. The method of claim 1, including obtaining a thirdconductivity measurement; and determining if water hardness hassignificantly increased, and when such determination is positive,initiating a remedial action.
 4. The method of claim 1, wherein theplurality of values further includes a first predetermined conductivityslope, representing the rate of increase of conductivity as a chelant isadded when there are non-sequestered hard water ions in the chamber; andwherein the plurality of values further includes a second predeterminedconductivity slope, representing the rate of increase of conductivity asa chelant is added when there are no non-sequestered hard water ions inthe chamber.
 5. A system for dispensing a chelant and a cleaning agent,comprising: a chelant source; a detergent source; a conductivity sensor;and a control system configured to, determine a first chelant amountbased on a first conductivity measurement received from the conductivitysensor; add the first chelant amount to a chamber from the chelantsource; determine a chelant factor based on a plurality of values,including the first conductivity measurement, a second conductivitymeasurement received from the conductivity sensor, and the first chelantamount, wherein the chelant factor corresponds to a fraction of waterconductivity due to hard water ions; store the chelant factor; add anamount of detergent to the chamber from the detergent source; and afterstoring the chelant factor: determine an additional amount of wateradded to the chamber; determine a second chelant amount in accordancewith the additional amount of added water and the chelant factor; andadd the second chelant amount to the chamber.
 6. The system of claim 5,wherein the control system is configured to determine as the firstchelant amount an amount of chelant that is projected to be sufficientto fully sequester hard water ions in the chamber.
 7. The system ofclaim 5, wherein the plurality of values further includes a firstpredetermined conductivity slope, representing the rate of increase ofconductivity as a chelant is added when there are non-sequestered hardwater ions in the chamber; and wherein the plurality of values furtherincludes a second predetermined conductivity slope, representing therate of increase of conductivity as a chelant is added when there are nonon-sequestered hard water ions in the chamber.